The use of foamed liquids has become increasingly important in a number of industrial fields, among them the cleaning of condensers, heat exchangers, storage tanks, and other large-volume vessels employed in power generators, chemical processing, petroleum refining, and other industries. This phenomenon is due in part to the rising costs of the liquids employed in such cleaning, and in part to the increasingly difficult problems encountered in disposing of large volumes of such liquids after the cleaning operation has been completed. In addition, many devices cannot be cleaned with a liquid as they are not structurally capable of bearing its weight. Additionally, foams have become important in petroleum well stimulation and fracturing. The use of a foam rather than a liquid in the latter applications requires less pumping capacity for the high pressure injection of the well treatment fluid, and lessens the possibility of formation damage, particularly in natural gas wells. As with industrial cleaning operations, the cost of the treatment fluids and fluid disposal problems after treatment increase the attractiveness of employing foams.
One of the major problems encountered in using foam for the above referenced and other applications is the difficulty of producing a substantially uniform foam without slugs of liquid or gas emulsion therein which lessen the stability and quality of the foam. Ideally, a foam has a uniform dispersion of fine gas bubbles in a relatively small volume of liquid. As the volume of liquid increases with respect to the volume of gas, the gas bubbles become spaced farther apart, resulting initially in a low stability foam, and, as the liquid to gas ratio is further increased, a gas emulsion results, having little or no structural stability. On the other hand, as the gas volume is increased with respect to the liquid volume, the crowding of the gas bubbles together results in deformation of the bubbles and an increase in the rigidity and therefore structural stability of the foam.
Prior to the present invention, there has been no way to reliably ensure, when producing large volumes of foam, that liquids and gas emulsions do not pervade the foam product, lowering its stability and hence its utility.